Manufacturing method for multi-component alloying steel with high strength and high wear-resistance and hot rolled plate thereof

ABSTRACT

This invention provides a manufacturing method of a multi-component alloying steel with high strength and high wear-resistance and a hot rolled plate thereof. The weight percentages of the chemical composition of the wear-resistant steel above is as follows: C: 1.0-1.2%, Si: 0.6-1.0%, Mn: 8.0-10.0%, P&lt;0.02%, S&lt;0.02%, Cr: 1.5-2.5%, Mo: 0.2-0.5%, V: 0.6-1.0%, Nb: 0.02-0.06%, Ti: 0.01-0.1%, Al: 0.03-0.08%, and the rest are Fe and unavoidable impurities. The manufacturing process of the hot rolled plate of the wear-resistant steel includes the steel making, continuous casting, heating, hot rolling and heat treatment.

BACKGROUND 1. Field of the Invention

This invention is related to a technical field of high strength and high wear resistant hot-rolled steel. In particular, this invention is related to a manufacturing method of multi-component alloying steel with high strength and high wear resistant and a hot rolled plate thereof.

2. Description of Related Art

At present, the widely used wear resistant steel in the coal-mining field is the medium and low alloy wear-resistant steels. The representative steels include the HARDOX series of Sweden (abbreviated as HD series below), EH series of JFE in Japan, NM series of Wuhan Iron and Steel Group Corp. and B-HARD series of Baosteel. The medium and low alloy wear-resistant steel is a type of low-carbon steel with the martensite or martensite-bainite complex microstructure after quenching and tempering. The wear resistance of this kind of wear resistant steel, especially the thick plate, is obviously attenuated from the surface to the heart, which is the main disadvantage of the martensite-bainite wear resistant steel. In addition, it is found that the applied effect of medium and low alloy martensite-bainite wear resistant steel is not ideal under the impact and fatigue working conditions in production practice. Although the medium and low alloy wear resistant steel has relatively good impact toughness, the fatigue stress cracking is easy to occur in this wear resistant steel during long-term service under the impacting wear condition, which will affect the service life. Served in the impact, wear and fatigue complex working conditions, the requirements for the comprehensive performance of the material are very high, including impact resistance, wear resistance, fatigue fracture toughness and fatigue crack sensitivity. At this time, the performance of low alloy wear resistant steel has been unable to meet the complex working conditions of coal mining.

The other widely used wear resistant steel is high manganese steel. Manganese wear-resistant steel has a long history and high safety performance. It has been widely used in all kinds of wear conditions, especially under the condition of impact abrasive wear. The application of manganese wear resistant steel in the mechanical equipment of coal mining is mainly the high manganese steel, which shows the quite special strengthening and wear resistant mechanisms. Under the larger impact load, deformation of materials in the superficial layer induces twin strengthening, dislocation tangles, etc., and the surface hardness and strength are improved rapidly. Meanwhile, the wear resistance, impact toughness, and fatigue crack growth rate of the high manganese steel after being strengthened are far superior to those of medium and low-alloy wear-resistant steel strengthened by the martensite or martensite-bainite phase change. However, in practical application, it is found that the impact energy provided in the coal mining process is not enough to fully exert deformation hardening ability of the high manganese steel. The hardening coefficient of high manganese wear resistant steel is low, and the degree of deformation hardening does not reach the ideal value. Therefore, the strengthening effect and wear resistance are not satisfactory in some typical application fields, such as the lining plate of ore crusher, material transport pipeline, bucket teeth of excavator and crawler board of middle trough of scraper conveyor.

When the coal mining machine is running in underground mine, the middle trough of scraper conveyer bears the violent friction of coal, scraper and chain, and is subjected to the effect of friction wear, such as abrasive wear, impacting wear and so on. In addition, the middle trough is also subjected to the action of the operating load of coal mining machine, lateral and longitudinal force of hydraulic support, extrusion and impact forces of large coal and rock blocks stuck in the middle trough. Therefore, the middle trough should have enough strength, stiffness and wear resistance.

SUMMARY

The aim of the present invention is to solve the problem of poor wear resistance and poor fatigue performance of wear resistant steel used in the above mechanical equipment under the medium and low impact loads.

The technical scheme adopted by this invention is as follows:

A multi-component alloying steel with high strength and high wear resistant is provided. The weight percentage of chemical composition or the wear resistant steel is as follows: C: 1.0-1.2%, Si: 0.6-1.0%, Mn: 8.0-10.0%, P<0.02%, S<0.02%, Cr: 1.5-2.5%, Mo: 0.2-0.5%, V: 0.6-1.0%, Nb: 0.02-0.06%, Ti: 0.01-0.1%, Al: 0.03-0.08%, and the rest are Fe and unavoidable impurities.

Further, the weight percentage of C is 1.01-1.19%.

Further, the weight percentage of Si is 0.61-0.98%.

Further, the weight percentage of Mn is 8.02-9.99%.

Further, the weight percentage of Cr is 1.55-2.47%. The weight percentage of Nb is 0.02-0.06%.

Further, the weight percentage of Mo is 0.22-0.49%. The weight percentage of Ti is 0.03-0.09%.

Further, the weight percentage of V is 0.61-0.98%. The weight percentage of Al is 0.03-0.07%.

Further, a method for manufacturing hot rolled plates of alloying steel with high strength and high wear-resistance, comprising processes of steel making, continuous casting, heating, hot rolling and heat treatment. During the continuous casting process, the casting temperature is 1370-1390° C., and a slab is obtained.

During the heating process, the holding temperature of the slab is 1160-1200° C.

During the hot-rolling process, the rolling temperature of the slab is 1000-1180° C.

During the heat treatment process of the hot rolled plate, the starting temperature of water toughening treatment is 1000-1070° C., and the stopping temperature of the water toughening treatment is 200-300° C.

Further, the tensile strength of the hot rolled plate is more than 900 MPa. The yield strength of the hot rolled plate is more than 480 MPa. The impact energy of V-notch impacts test for the hot-rolled plate is as follows: The impact energy (Akv) at 25° C. is more than 100 J. The impact energy (Akv) at −40° C. is 40-50 J. The Brinell hardness is 220-240 HB.

Further, the wear rate of hot rolled plate is less than 20×10⁻⁶ mm³/N·m under a condition of 200 N load sliding wear.

The steelmaking is proportioning according to the weight percentage as the following components: C: 1.0-1.2%, Si: 0.6-1.0%, Mn: 8.0-10.0%, P<0.02%, S<0.02%, Cr: 1.5-2.5%, Mo: 0.2-0.5%, V: 0.6-1.0%, Nb: 0.02-0.06%, Ti: 0.01-0.1%, Al: 0.03-0.08%, and the rest are Fe and unavoidable impurities.

The advantages and positive effects of the invention are as follows: a hot rolled medium manganese wear-resistant steel with high strength and high wear resistance is obtained by optimizing the composition and content of alloying elements and rationally adjusting the ratio of C and Mn elements. Moreover, the addition of Ti, V, Nb and other micro-alloying elements in steel can refine the crystal grains and form alloy carbides with C element. After solid solution treatment, these carbides disperse in crystal grains and obtain a second phase strengthening effect, which effectively increases the strength, hardness and wear resistance of steel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a photograph showing a metallographic structure of multi-component alloying steel with high strength and high wear resistant (200×).

FIG. 2 is a photograph showing a metallographic structure of multi-component alloying steel with high strength and high wear resistant (500×).

DESCRIPTION OF THE EMBODIMENTS

The idea of the alloy composition design for multi-component alloying steel with high strength and high wear resistant is to expand the austenite region by rationally adjusting the content of C and Mn elements, and the unstable single austenite structure is obtained at normal temperature. Moreover, the addition of a small amount of Cr, Mo, Nb, V and Ti elements can effectively restrain the austenite grain growth and refine the crystal grains. Meanwhile, these micro-alloying elements can form some alloying carbides with C element. These carbides disperse uniformly in solid solution substrate and play the role of second phase strengthening effect, which effectively increases the strength, hardness and wear resistance of steel of the medium manganese steel. When the steel plate is affected by the impact force in actual use, the martensitic transformation strengthening occurred in surface layer to rapidly increase the surface hardness, which further enhance the wear resistance.

In the following descriptions, the reasons for choosing the above chemical compositions and the content ranges will be explained in detail.

Carbon: C element is one of the main added ingredients. The solubility of carbon in austenite is high, which is beneficial to the stability of austenite phase. At the same time, the carbon can form the carbides with the added trace alloying elements. During solution treatment, the dispersed carbide particles in crystal grains form the better solid solution strengthening effect, which increases the hardness, strength and wear resistance of wear resistant steel. But, when the carbon content is more than 1.5%, the carbides in cast microstructure increase. Despite of the water toughening treatment, the retained carbides in austenite are still more. These carbides distribute along the grain boundary to reduce the mechanical properties of steel and improve the austenite stability, which is not conducive to obtaining the microstructure of unstable austenite. In order to reduce the stability of austenite, according to the carbon content of high manganese steel of 1.0-1.4%, the carbon content of the invention is 1.0-1.2%, and the optimum carbon content is 1.01-1.19%.

Manganese: Mn element is one of the main added ingredient, which is favorable for stabilizing austenite and enlarging the austenite phase area. Meanwhile, the element of Mn increases the hardenability of steel and decreases the critical cooling rate of martensite formation. When the content of Mn is increased, the strength and impact toughness of high manganese steel are improved, which is because Mn has the effect of increasing intergranular binding force. But the over-high Mn content will decrease the thermal conductivity of steel and affect the mechanical properties of steel. In order to obtain metastable austenite structure at room temperature, the Mn content of the invention is 8.0-10.0%, preferably 8.02-9.99%, in combination with Fe—Mn—C phase diagram.

Silicon: Si element plays the role of deoxidation and solid solution strengthening in steel and the increase of Si content is beneficial to the strength and hardness of steel. The over-high content of Si will decrease the toughness of steel, and a silicon oxide layer is formed on the surface of steel plate. When the steel plate is heated, the viscosity of the oxide skin is larger, and the phosphorus removal is difficult after the steel plate is removed outside the furnace, which causes the serious red oxide skin on the surface of hot rolled steel, which results in poor surface quality and poor welding properties of the hot rolled steel. The Si content of this invention is 0.6-1.0%, preferably 0.61-0.98%.

Sulfur and phosphorus: S and P elements are unavoidable impurity elements in steel, which are unfavorable to the plasticity and toughness of steel. So the contents of S and P should be as less as possible. In consideration of the actual level of steel-making, the content of S and P in this invention is less than 0.02%.

Chromium: The solubility of Cr in austenite is very high, which improves the stability of austenite and accelerates the precipitation of carbides in the cooling. The carbides formed by Cr and C elements are dissolved in austenite, which improves the strength, hardness and wear resistance of steel. The Cr content in this invention is 1.5-2.5%, preferably 1.55-2.47%.

Aluminum: Al is a strong deoxidizing element. In order to ensure the lower oxygen content in the steel, the content of Al in the invention is 0.03-0.08%. After deoxidizing, the superfluous Al element can form MN alloy phases with N element in steel, which increases the strength of steel and refines the austenite grains.

Molybdenum, Titanium, Vanadium, Niobium: Mo, Ti, V and Nb elements have strong affinity with C element, which can replace the Fe atoms in cementite and form the alloy cementite and increase the stability of the cementite. At the same time, these elements can form some new alloy carbides. After solid solution treatment, these alloy carbides disperse in the grains and play the role of the second phase strengthening to increasing the strength, hardness and wear resistance of steel, and refine the grains. But the over-high contents of these elements can lead to a great decrease in plasticity. So, the Mo content in this invention is 0.2-0.5%, preferably 0.22-0.49%. The content of Ti is 0.01-0.1%, preferably 0.03-0.09%. The content of V is 0.0-1.0%, preferably 0.61-0.98%. The content of Nb is 0.02-0.06%.

In order to better understand this invention, the contents of this invention are further clarified in combination with some embodiments. But the contents of this invention are not limited by the following embodiments.

1. Ten different compositions were selected. The specific ratios of each component are shown in Table 1.

TABLE 1 Weight percentages of the compositions of examples (%) Exampl C Si Mn P S Cr Mo V Nb Ti Al 1 1.02 0.94 9.99 0.018 0.012 1.55 0.22 0.61 0.027 0.04 0.037 2 1.02 0.72 8.84 0.016 0.011 2.15 0.47 0.67 0.043 0.06 0.070 3 1.04 0.98 9.52 0.017 0.012 1.87 0.31 0.72 0.036 0.05 0.046 4 1.04 0.64 9.38 0.013 0.009 2.36 0.27 0.62 0.028 0.03 0.057 5 1.06 0.85 9.22 0.015 0.012 2.43 0.49 0.68 0.060 0.07 0.051 6 1.06 0.62 9.07 0.012 0.009 2.25 0.37 0.73 0.041 0.04 0.065 7 1.08 0.83 8.90 0.017 0.010 2.36 0.27 0.60 0.034 0.08 0.041 8 1.08 0.63 8.81 0.016 0.013 1.99 0.33 0.65 0.020 0.09 0.056 9 1.15 0.81 8.31 0.012 0.009 1.64 0.25 0.84 0.023 0.06 0.043 10 1.19 0.61 8.02 0.014 0.011 2.47 0.45 0.95 0.057 0.04 0.030

The hot rolled plates of the ten examples were sampled and analyzed. After sanding, polishing and corrosion, the microstructure was observed under the metallographic microscope. It was identified as a single austenitic structure. A small amount of granular carbides was dispersed and distributed in the grain boundaries, and the grain size was smaller after hot rolling.

2. The samples of the ten examples were processed by the process flow of melting, continuous casting, heating, hot rolling, and heat treatment. The processing parameters of each sample are shown in Table 2.

TABLE 2 Technical parameters of ten groups of examples Starting stopping Continuous Slab Starting Finishing temperature temperature casting reheating rolling rolling of water of water temperature/ temperature/ temperature/ temperature/ toughening/ toughening/ Example ° C. ° C. ° C. ° C. ° C. ° C. 1 1372 1162 1060 1006 1000 200 2 1375 1168 1085 1014 1005 242 3 1380 1170 1094 1020 1018 225 4 1382 1174 1118 1038 1020 258 5 1385 1178 1136 1046 1034 270 6 1390 1182 1150 1054 1048 285 7 1388 1184 1168 1068 1052 291 8 1384 1188 1180 1078 1064 300 9 1377 1194 1174 1070 1056 260 10 1374 1198 1155 1060 1048 288

3. The mechanical properties of the final hot rolled plates of the ten examples are shown in Table 3.

TABLE 3 Mechanical properties hot rolled plates of the ten examples Yield Tensile Impact energy strength/ strength/ Akv(J) Example MPa MPa 25° C. −40° C. HB 1 480 900 102 41 220 2 503 920 123 48 221 3 497 912 100 40 223 4 485 915 116 44 225 5 507 923 109 42 234 6 521 946 127 50 237 7 504 916 113 47 223 8 511 932 114 46 235 9 503 925 103 41 232 10 518 942 101 40 240

It can be seen from Table 3 that the tensile strengths of the ten samples were more than 900 MPa and the yield strengths were more than 480 MPa. The impact energies of V notches test are as follows: Akv is more than 100 J at 25° C. and Akv is 40-50 J at −40° C. The Brinell hardness is 220-240 HB. By comparison, the comprehensive mechanical properties of the example six are the highest.

4. Friction and Wear Properties

M2000 friction and wear tester was used to study the friction and wear properties. The test conditions are as follows: The size of experimental samples was 10×10×20 mm. The friction pair was GCr15 steel ring having a diameter of 40 mm. The applied load was 200 N and the rotational speed of the steel ring was 200 rpm. The wear test time was 2 h. The wear rate was calculated by the volume wear rate, and the calculation formula is as follows: KV=Δm/ρ·P·L.

Where, KV is the volume wear rate (mm³/N·m), Am is the weight loss (mg), p is the material density (7.89 g/cm³), P is an applied load (N) and L is the wear distance (m).

The results of wear rates for the ten examples are shown in Table 4.

-   -   Table 4: Comparison of wear rates for ten examples with samples         of HARDOX450 and Mn13

TABLE 4 Comparison of wear rates for ten examples with samples of HARDOX450 and Mn13 Sample HAR DOX Mn 1 2 3 4 5 6 7 8 9 10 450 13 Wear rate 19.91 19.83 19.74 19.65 19.46 19.23 19.41 19.52 19.59 19.40 40.21 44.83 (10⁻⁶ mm³/N · m)

It can be seen from Table 4 that the wear rates of the ten examples are close. The wear resistance is increased to 2.02 times and 2.25 times than the wear resistance of the samples of HARDOX450 and Mn13, respectively.

The above description has explained in detail for the examples of this invention, but the content stated is only the better embodiment of the invention. It cannot be considered to a limitation of the implementation scope of the invention. All equivalent changes and improvements on the basis of the application scope of this invention should be still within the claimed scope of this patent. 

1-10. (canceled)
 11. A multi-component alloying steel with high strength and high wear-resistance, wherein a composition of the steel comprises: 1.0-1.2 wt % of C; 0.6-1.0 wt % of Si; 8.0-10.0 wt % of Mn; <0.02 wt % of P; <0.02 wt % of S; 1.5-2.5 wt % of Cr; 0.2-0.5 wt % of Mo; 0.6-1.0 wt % of V; 0.02-0.06 wt % of Nb; 0.01-0.1 wt % of Ti; 0.03-0.08 wt % of Al; and Fe and unavoidable impurities, which account for the rest amount of the composition.
 12. The steel of claim 11, wherein a content of the C is 1.01-1.19 wt %.
 13. The steel of claim 11, wherein a content of the Si is 0.61-0.98 wt %.
 14. The steel of claim 11, wherein a content of the Mn is 8.02-9.99 wt %.
 15. The steel of claim 11, wherein a content of the Cr is 1.55-2.47 wt %, and a content of the Nb is 0.02-0.06 wt %.
 16. The steel of claim 11, wherein a content of the Mo is 0.22-0.49 wt %, and a content of the Ti is 0.03-0.09 wt %.
 17. The steel of claim 11, wherein a content of the V is 0.61-0.98 wt % and a content of the Al is 0.03-0.07 wt %.
 18. A method of manufacturing a hot rolled plate of the steel of claim 11, the method comprising: performing a steel making step to the steel; performing a continuous casting step to the steel at a temperature of 1370-1390° C. to obtain a slab; performing a heating step to the slab, wherein a holding temperature of the slab is 1160-1200° C.; performing a hot rolling step to the slab, wherein a rolling temperature of the slab is 1000-1180° C.; and performing a heat treatment to the slab, wherein the heat treatment comprises a water toughening step started at a temperature of 1000-1070° C. and stopped at a temperature of 200-300° C.
 19. A hot rolled plate formed by the method of claim 18, wherein the hot rolled plate having properties below: a tensile strength of more than 900 MPa; a yield strength of more than 480 MPa; an impact energy (Akv) of more than 100 J at 25° C. and 40-50 J at −40° C. obtained by V-notch impact test; and a Brinell hardness of 220-240 HB.
 20. The hot rolled plate of claim 19, wherein the hot rolled plate further has a wear rate of ≤20×10⁻⁶ mm³/N·m under 200 N load sliding wear condition. 